Conventionally, management information is recorded in a bar-code form on an inner track of a DVD optical disk, and is used to manage the optical disk.
The management information includes information to inhibit copying data, and identification information unique to the optical disk. As shown in FIG. 1(A), a high-power laser beam from a YAG laser is directed to an inner track inside of the ordinary data recording area of the optical disk, thereby recording the management information by successively evaporating a material on an information recording surface in radial directions. In an ROM disk, the high-power laser beam evaporates a reflective aluminum film. In a recordable disk, the high-power laser beam evaporates a color film and a reflective film (of Au, Ag, etc.). In a rewritable disk, the high-power laser beam evaporates a phase-change film and a reflective film (of Au, Ag, etc.).
In DVD-ROM and DVD-RAM optical disks, the management information is recorded on a BCA (Burst Cutting Area). The BCA is formed within a range of from 22.3 (+0 and −0.8) through 23.5 (+0.1, −0.1) [mm] from the center hole of the disk. In DVD-R and DVD-RW optical disks, the management information is recorded on an NBCA (Narrow Burst Cutting Area). In the DVD-R optical disk, the NBCA is formed within a range of from 22.71 (+0.06, −0.06) through 23.51 (+0.06, −0.06) [mm], and in the DVD-RW optical disk, the NBCA is formed within a range of from 22.7 (+0.05, −0.05) through 23.5 (+0.05, −0.05) [mm].
The management information is recorded using the RZ modulation, and a playback signal RF (see FIGS. 1(B)–1(E)) obtained with tracking servo control deactivated is binarized and played back.
The above-mentioned BCA and NBCA ares are pre-pit areas in the DVD-ROM and DVD-RAM optical disks where embossed pits are formed beforehand. In these optical disks, a variation in signal level due to pits (the variation in the signal level having a short period as shown in FIG. 1(C)) is superimposed on the playback signal RF (BCA) (see FIGS. 1(B) and 1(C)) obtained when the management information is played back. In contrast, in the DVD-R and DVD-RW optical disks having no pits in the concerned area thereof, no similar variations are observed in the playback signal RF (NBCA) (see FIGS. 1(D) and 1(E)) when the management information is obtained. Referring to FIGS. 1(C) and 1(E), T1 is 3±1.5 [μsec], and T2 is 8.89n±2 [μsec], where n is 1, 2, 3 or 4.
The optical disk apparatus that records data to and/or plays back data from a variety of these optical disks must reliably play back data from any of these optical disks.
The playback signal RF obtained from the BCA and NBCA where the management information is recorded has features different from disk type to disk type and from disk to disk. Specifically, the playback signal obtained from the BCA and NBCA varies in the degree of modulation from disk to disk. When the optical disk is decentered, the modulation by the surface of a mirror changes (a variation in the signal level having a large period as shown in FIGS. 1(B) and 1(D)).
In these optical disks, it is difficult to set an appropriate binarization threshold value when the playback signal obtained from the BCA and NBCA is binarized. Consequently, a reliable playback of the management information from a variety of these optical disks is difficult.